Sickle cell anemia is an autosomal recessive disorder and the most common genetic disease affecting African-Americans. Approximately 0.15% of African-Americans are homozygous for sickle cell disease, and 8% have sickle cell trait. Acute pain crisis, acute chest syndrome (ACS), and secondary pulmonary hypertension are common complications of sickle cell anemia. Inhaled nitric oxide (NO) has been proposed as a possible therapy for both primary and secondary pulmonary hypertension. Furthermore, a number of recent studies have suggested that NO may have a favorable impact on sickle red cells at the molecular level and could improve the abnormal microvascular perfusion that is characteristic of sickle cell anemia. This clinical trial is designed 1) to determine the pathophysiologic processes that are associated with and potentially contribute to secondary pulmonary hypertension in adult patients with sickle cell anemia. 2) to determine the relative acute vasodilatory effects of oxygen, intravenous prostacyclin, and inhaled nitric oxide on pulmonary artery pressures and other hemodynamic parameters in patients with secondary pulmonary hypertension and sickle cell anemia, and 3) to determine the effects of two months of inhaled nitric oxide on pulmonary artery pressures, other hemodynamic parameters, exercise tolerance, and symptoms in this patient population.